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Chemistry 30

Chemistry 30 · Worksheets

Diploma-style challenge

Ten questions of mixed difficulty, covering Acids and bases, Electrochemical cells, Equilibrium, Organic chemistry, Redox reactions, Thermochemistry. Print it, or work through it on screen — the answer key starts on its own page.

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Diploma-style challenge

Chemistry 30 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. A redox reaction is spontaneous when the standard cell potential, E°cell, is

    1. a) greater than 1.00 V
    2. b) zero
    3. c) positive
    4. d) negative

  2. In a voltaic cell, electrons travel through the external wire from the

    1. a) cathode to the anode
    2. b) salt bridge to the anode
    3. c) anode to the cathode
    4. d) solution to the electrodes

  3. A solution has [OH⁻] = 1.0 × 10⁻⁵ mol/L. Its pH at 25 °C is

    1. a) 14.00
    2. b) −5.00
    3. c) 5.00
    4. d) 9.00

  4. A current of 2.00 A flows for 30.0 min through a solution of Cu²⁺. The mass of copper deposited is closest to

    1. a) 2.37 g
    2. b) 0.59 g
    3. c) 1.19 g
    4. d) 4.74 g

  5. How much heat is absorbed when 100.0 g of water is warmed from 20.0 °C to 30.0 °C? (c = 4.19 J/(g·°C))

    1. a) 41.9 kJ
    2. b) 4.19 kJ
    3. c) 0.419 kJ
    4. d) 12.6 kJ

  6. A reaction has K = 4.0 × 10⁻³ at a given temperature. At equilibrium the mixture

    1. a) contains mostly products
    2. b) has completely reacted
    3. c) contains equal amounts of each
    4. d) contains mostly reactants

  7. The IUPAC name for CH₃CH=CHCH₂CH₃ is

    1. a) 2-pentene
    2. b) 3-pentene
    3. c) 2-pentane
    4. d) 1-pentene

  8. A cell is built from Zn²⁺/Zn (E° = −0.76 V) and Cu²⁺/Cu (E° = +0.34 V). The standard cell potential is

    1. a) +1.10 V
    2. b) −0.42 V
    3. c) −1.10 V
    4. d) +0.42 V

  9. A strong acid is one that

    1. a) has a pH below 1
    2. b) ionizes completely in water
    3. c) is very concentrated
    4. d) reacts quickly with metals

  10. How many moles of electrons are needed to produce 1 mol of aluminum from Al³⁺?

    1. a) 3 mol
    2. b) 1 mol
    3. c) 2 mol
    4. d) 27 mol

Answer key · Diploma-style challenge

Chemistry 30 · maddyhelps.com

  1. c) positive — A positive E°cell means the reaction can drive electrons through a circuit on its own. A negative value means the reverse reaction is the spontaneous one, and zero means the system is at equilibrium.
  2. c) anode to the cathode — Electrons are released by the oxidation at the anode and consumed by the reduction at the cathode, so they flow anode to cathode through the wire. Ions, not electrons, move through the solution and salt bridge.
  3. d) 9.00 — pOH = −log(1.0 × 10⁻⁵) = 5.00, so pH = 14.00 − 5.00 = 9.00. Answering 5.00 is forgetting to convert pOH to pH — and a hydroxide concentration that high should give a basic pH.
  4. c) 1.19 g — q = It = (2.00 A)(1800 s) = 3600 C. Moles of electrons = 3600 ÷ 96500 = 0.0373 mol. Cu²⁺ needs 2 electrons each, so 0.0187 mol of Cu × 63.55 g/mol = 1.19 g. Forgetting to divide by 2 gives the 2.37 g distractor.
  5. b) 4.19 kJ — q = mcΔT = (100.0 g)(4.19 J/(g·°C))(10.0 °C) = 4190 J = 4.19 kJ. ΔT is the change in temperature, not the final temperature.
  6. d) contains mostly reactants — K far below 1 means the denominator — the reactants — dominates. The reaction barely proceeds before it settles, which is why a small K is described as favouring reactants.
  7. a) 2-pentene — Five carbons with a double bond gives pentene. Numbering from the nearer end puts the double bond between carbons 2 and 3, and it is named for the lower of those two numbers.
  8. a) +1.10 V — Copper has the higher reduction potential, so it is reduced at the cathode and zinc is oxidized: E°cell = E°cathode − E°anode = 0.34 − (−0.76) = +1.10 V. The positive value confirms the cell runs on its own.
  9. b) ionizes completely in water — Strength is about how completely an acid ionizes, not how much of it is dissolved. A dilute solution of HCl is still a strong acid; a concentrated solution of acetic acid is still a weak one.
  10. a) 3 mol — Al³⁺ + 3e⁻ → Al, so each aluminum atom needs three electrons. That is why producing aluminum by electrolysis uses so much electricity.